Automatic screen and keypad brightness adjustment on a mobile handheld electronic device

ABSTRACT

A method is set forth for automatically adjusting screen and keypad brightness on a mobile electronic device having a light sensor, display screen and keypad, for optimum legibility under varying lighting conditions, with minimal eye strain and distraction to the user. The method includes obtaining light level samples from the light sensor, and independently adjusting backlight intensity of the display screen and keypad responsive to the light level samples. Preferably, correct screen and keypad adjustments are made responsive to the user pulling his or her handheld device out of its holster notwithstanding non-optimal ambient light detection while the device is being removed from the holster. According to another aspect, the described method allows for ambient light detection in a handheld device where the light sensor and a message notification indicator share a common light pipe.

FIELD

The present application relates generally to electronic devices and moreparticularly to a method for automatically adjusting screen and keypadbrightness on a mobile electronic device.

BACKGROUND

Liquid crystal display (LCD) screen and keypad brightness on a handheldelectronic device may be adjusted for different operating environmentsin order to provide an optimal user experience. For example, in outdooror sunlight conditions the LCD backlight must be very bright in order tobe readable, and the keypad backlight should be off to conserver batterypower. In normal indoor or office conditions, the LCD backlight shouldoperate at medium brightness while the keypad backlight is usuallyturned off. In dim or dark conditions, the LCD backlight must be at lowintensity so as to avoid eye strain and the keypad backlight must be on.

Ambient lighting conditions can change rapidly as the user moves betweendifferent working environments. For example, walking from indoors tooutdoors may render the LCD screen immediately unreadable unless the LCDbacklight brightness is increased. Conversely, when the user moves froma bright environment into a dimly lit room, the keypad may be unreadableunless the keypad backlight is turned on.

Prior art arrangements have been implemented in GPS displays and laptopcomputers for providing basic automatic screen and keypad backlightingadjustment. However, none of such prior art backlighting algorithms areknown to address independent control of LCD and keypad backlightingadjustment as a user moves between different ambient lightingconditions. Moreover, none of the known prior art addresses the problemof providing rapid backlight adjustment in response to a user removinghis or her handheld electronic device from a wearable holster accessory,or the problem of detecting ambient light when the light sensor andmessage notification indicator for the device share a common light pipe,such as described in co-pending U.S. patent application Ser. No.11/187,867, filed Jul. 25, 2005, and entitled SHARED LIGHT PIPE FOR AMESSAGE INDICATOR AND LIGHT SENSOR.

BRIEF DESCRIPTION OF THE DRAWINGS

The method for automatically adjusting screen and keypad brightness on amobile handheld electronic device will be better understood withreference to the following description and to the Figures, in which:

FIG. 1 is a representation of a mobile handheld electronic device inconnection with which a method for automatically adjusting screen andkeypad brightness is set forth in accordance with one embodiment;

FIG. 2 is a block diagram of certain internal components within theelectronic device of FIG. 1;

FIG. 3 is a flowchart showing steps in a method for automaticallyadjusting screen brightness in the electronic device of FIG. 1;

FIG. 4 is a flowchart showing steps in the method of FIG. 3 when theelectronic device is in DIM mode;

FIG. 5 is a flowchart showing steps in the method of FIG. 3 when theelectronic device is in OFFICE mode;

FIG. 6 is a flowchart showing steps in the method of FIG. 3 when theelectronic device is in BRIGHT mode;

FIG. 7 is a flowchart showing steps for automatically adjusting keypadbrightness in the electronic device of FIG. 1;

FIG. 8 is a flow chart showing steps for controlling sample rate for themethods of FIGS. 3 and 7.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring to FIG. 1, a mobile handheld electronic device is indicatedgenerally by the numeral 20. In the present embodiment, the electronicdevice 20 is based on the computing environment and functionality of awireless personal digital assistant. It will be understood, however,that the electronic device 20 is not limited to a wireless personaldigital assistant. Other electronic devices are possible, such asdesktop computers, cellular telephones, GPS receivers, smart telephones,and laptop computers. Referring again to the present embodiment, theelectronic device 20 includes a housing 22 that houses a mechanicalvibration means (not shown) and frames an LCD display 24, a speaker 26,a message notification indicator 28, a track wheel 30, an exit key 32and a keypad 34. Preferably, the message notification indicator 28 is inthe form of a light pipe having two internal branches terminatingrespectively in a Light Emitting Diode (LED) and an ambient lightsensor, as set forth in co-pending U.S. patent application Ser. No.11/187,867, filed Jul. 25, 2005, and entitled SHARED LIGHT PIPE FOR AMESSAGE INDICATOR AND LIGHT SENSOR, the contents of which areincorporated herein by reference. The track wheel 30 and the exit key 32can be inwardly depressed along the path of arrow “A” as a means ofproviding additional user-input. The housing 22 is made from a suitablematerial as will occur to those skilled in the art, and can be stored,for example, in a holster (not shown) that includes an attachment forattaching to a user's belt.

Referring now to FIG. 2, a block diagram is provided of certain internalcomponents within the device 20. The device 20 is based on amicrocomputer including a processor 36 connected to a read-only-memory(ROM) 38 that contains a plurality of applications executable by theprocessor 36 for enabling the device 20 to perform certain functions.The processor 36 is also connected to a random access memory unit (RAM)40 and a persistent storage device 42 which are responsible for variousnon-volatile storage functions of the device 20. The processor 36receives input from various input devices including the track wheel 30,the exit key 32, and the keypad 34. The processor 36 outputs to variousoutput devices including the LCD display 24, the speaker 26, theindicator 28 and the mechanical vibration device 32. The processor 36 isalso connected to an internal clock 44 and a modem and radio device 46.The modem and radio device 46 are used to connect to various wirelessnetworks using an antenna 48.

Reference is now made to FIG. 3, showing a flowchart of a method forautomatically adjusting screen 24 and keypad 34 brightness on the mobilehandheld electronic device of FIGS. 1 and 2. The method is implementedby an algorithm within an application executable by the processor 36 tocorrectly switch between three screen-specific ambient lighting modes(referred to herein as DIM, OFFICE and BRIGHT, respectively) and twokeypad-specific ambient lighting mode (referred to herein as KEYPAD-ONand KEYPAD-OFF, respectively. The screen-specific modes are determinedindependently of the keypad-specific modes. In DIM mode, the screen 24backlight is dimmed for low lighting environment. In OFFICE mode, thescreen 24 backlight is set to a brightness suitable for an officeenvironment. In BRIGHT mode, and the screen 24 backlight is set at fullbrightness, suitable for legibility in bright sunlight (as indicatedbelow, KEYPAD-OFF mode is enabled whenever BRIGHT mode is enabled). InKEYPAD-ON mode, the keypad backlight is turned on. In KEYPAD-OFF mode,the keypad backlight is turned off. The DIM, OFFICE, BRIGHT, KEYPAD-ONand KEYPAD-OFF modes are determined by detected ambient light conditionsand operate to set the backlights to appropriate operating states, asdiscussed in greater detail below.

Each ambient lighting mode has a corresponding brightness/state value asset forth in Table A, where “% PWM” represents the duty cycle of a pulsewidth modulated signal of variable base frequency dependent on thespecified duty cycle, and “Lux range” represents the range of ambientlighting intensity (measured in Lux units, where Lux represents theamount of visible light per square meter incident on a surface) in whicheach mode operates:

TABLE A Screen Backlight Mode DIM mode OFFICE mode BRIGHT mode Lux range<70 16 < Lux < 4400 3000 < Lux of ambient lighting Screen 3%-6.5% PWM10%-40% PWM 100% PWM backlight (based on 10%- (based on 10%-100% (this“overdrives” brightness 100% brightness brightness defined in thebacklight defined in Screen/Keyboard circuit) Screen/Keyboard optionsscreen) options screen) Keypad Backlight Mode KEYPAD-ON KEYPAD-OFF Luxrange for ambient <250 >60 lighting Keypad backlight state ON OFF

As indicated in Table A, the screen 24 backlight is adjustable in 5 or10 discreet steps between 3% and 6.5% PWM, an additional 5 or 10discreet steps between 10% and 40% PWM and may also be set to 100% PWMBacklight brightness control also permits a smoothly and quick fade(˜200 ms) and a slow fade (1-1.5 s) between any of these steps (inaddition to the off state). The keypad 34 backlight is adjustable in atleast 5 discreet steps between 0% and 100% PWM, allowing for a smoothquick fade (200 ms) and a very slow fade (4-5 seconds, ideally) betweeneach of these discreet levels and the off state.

Upon starting the algorithm (step 50) when the device 20 is turned on,the backlight mode is normally initialized to an appropriate mode usingthe ambient lighting sensed by the light sensor at that time. Next,light sensor samples are taken at set intervals and maintained in abuffer containing the five most recent samples at any given time (step52). This buffer is referred to as the sample window because it is amoving window such that when each new sample is received, the oldestsample in the window is discarded from the buffer. The amount of timebetween each light sensor sample determines the sampling rate. A typicalsampling rate is one sample per 1.2 seconds although in some situationsthe sampling rate may be increased to 400 ms temporarily for 5 samplesto facilitate quick adjustment of the screen and keypad backlights. Atstep 54, the median sample value is calculated by sorting all samples inthe sample window and choosing the middle value (i.e. the third samplein the window).

When each sample is received, a new median in the sample window iscalculated and compared to various thresholds (step 56) to determine ifa backlight adjustment is necessary, according to the thresholds listedin state Table B, where ADC represents Analog to Digital Converteroutput values:

TABLE B median light sensor ADC current mode current mode current modevalue is DIM is OFFICE is BRIGHT <= 7 n/a Switch to DIM Switch to DIM >=14 switch to n/a n/a OFFICE <= 450 n/a n/a Switch to OFFICE >= 650switch to Switch to BRIGHT n/a BRIGHT Keypad backlight modes are handledindependently from the LCD backlight modes: current mode is KEYPAD-ONcurrent mode is KEYPAD-OFF < = 16 n/a switch to KEYPAD-ON >50 for 30switch to KEYPAD-OFF n/a seconds

The relationship between ADC threshold values expressed in Table B andlight intensity values is as follows: ADC 7=16 Lux, ADC 14=70 Lux, 16ADC=60 Lux, 50 ADC=250 Lux, ADC 450=3000 Lux, and ADC 650=4400 Lux.Operation of the state Table B is depicted in the flowcharts of FIGS. 4,5 and 6.

Thus, as shown in FIG. 4, when the backlighting is in DIM mode, themedian sample value is compared (step 58) to a threshold value of 14 (70Lux) and if the value is greater than 14 OFFICE mode of backlightoperation is selected (step 62) wherein the screen 24 backlight is at abrightness suitable for an office environment. However, if the mediansample value is greater than 650 (step 64) then BRIGHT mode of backlightoperation is selected (step 66) wherein the screen 24 backlight is setto full brightness.

As shown in FIG. 5, when the backlighting is in OFFICE mode (step 68),the median sample value is compared (step 70) to a threshold value of 7(16 Lux) and if the value is less than 7 DIM mode of backlight operationis selected (step 72) wherein the screen 24 backlight is dimmed.However, if the median sample value is greater than 650 (step 74) thenBRIGHT mode of backlight operation is selected (step 76) wherein thescreen 24 backlight is set to full brightness.

As shown in FIG. 6, when the backlighting is in BRIGHT mode (step 78),the median sample value is compared (step 80) to a threshold value of 7and if the value is less than 7 DIM mode of backlight operation isselected (step 82) wherein the screen 24 backlight is dimmed. If themedian sample value is less than 450 (step 84) then OFFICE mode ofbacklight operation is selected (step 86) wherein the screen 24backlight is at a brightness suitable for an office environment.

From FIGS. 4 and 5, it will be noted that the threshold for changingfrom DIM mode to OFFICE mode is higher than the threshold for changingfrom OFFICE to DIM mode. This compensates for situations where theambient lighting is hovering around a particular threshold value andprevents constant transitioning between backlight states. A similarhysteresis is integrated into the threshold values between the OFFICEand BRIGHT modes (FIGS. 5 and 6).

As indicated above, keypad 34 lighting is controlled independently ofscreen 24 backlighting to allow the keypad to respond more quickly todim environments, and to allow the LCD screen to respond more quickly tooffice and bright or sunlight environments. Hence, it is possible forthe screen backlight to be in OFFICE or BRIGHT mode while the keypadbacklight is still in KEYPAD-ON mode (temporarily). As set forth in FIG.7, while the keypad backlight is OFF (step 88), each sample value(rather than the median sample value) is compared (step 90) to athreshold value of 16 and if the value is less than 16 the keypad 34backlight turns on right away (step 92). This ensures that the user doesnot have to wait to type if they are unable to see the keypad 34. Thismeans that the keypad may sometimes turn on prematurely when the device20 is not actually in a dim or dark environment but a single sample lessthan 16 is received for some reason. This ensures that the keypad 34 isnever unusable, even though slightly more battery is drawn and the usermay become slightly confused as to why the keypad backlight appears toturn on “randomly” in some circumstances. Ideally, the keypad 34 shouldturn on quickly (about 200 ms) after receiving a single “dim” sample butfade off very slowly so that it is barely noticeable (e.g. 5-10seconds). This helps to remove distraction (and possible confusion) whenthe LCD screen 24 backlight is turned off.

While the keypad backlight is ON, consecutive sample values are compared(step 94) to a threshold value of 50 and once 30 seconds of contiguoussamples greater than 50 have been received the keypad 34 is turned OFF(step 88). This avoids the possibility of “thrashing” the keypadbacklight on and off in highly variable lighting environments, whichwould be quite distracting and annoying to the user.

By using the median sample in the sample window for mode-changedecisions, brief lighting fluctuations (e.g. bright flashes lasting lessthan about 800 ms) are effectively filtered out while still providing anacceptably quick response to entering an area with bright sunlight orpulling the device out of the holster in bright sunlight. Transitioningthrough a dim environment for less than about 5 seconds is also ignoredbecause all five samples in the sample window are required to be lessthan the threshold value for the currently active mode to affect a modechange. Since it takes several seconds for a user's eyes to adjust to adimmer environment, the LCD screen 24 brightness is permitted by thealgorithm to adjust gradually.

As shown in FIG. 8, light sensor samples are not taken (i.e. sleep mode)while the device 20 is off or in the holster (step 100) in order to savebattery life and because samples are not likely to be valid because thelight sensor is likely covered by an arm (device 20 is in holster) or ina bag or a pocket. When the light sensor software “wakes up” (step 102),sampling and backlight adjustment begins (step 106) with a fast samplingrate (400 ms) for the next five samples. The first sample received isused to initialize the entire sample window, if the second sample isbrighter than the first, then this value is used to initialize theentire sample window. If the third sample is brighter than the firsttwo, then it is used to initialize the sample window.

Thereafter, the normal sampling rate is one sample every 1.2 seconds(step 108). Preferably, each light sensor sample is actually an averageof multiple quick samples taken over a period of about 9 ms. Moreparticularly, at least 8 ADC readings are taken over a 9 ms period sothat they can be averaged out so as to increase the reliability of eachsample and filter out small variances in AC indoor lighting.

When the device 20 is pulled out of its holster, removed from a pocketor bag, etc., it is highly likely that the light sensor will betemporarily partially covered by the user's hand or shirt. This meansthat the first couple samples could be below the threshold fortransitioning to DIM mode, even if the device 20 is operating in theOFFICE mode. Likewise, the first couple of samples could be indicativeof OFFICE mode even though the device is in a bright environment.However, it is nearly impossible for a brighter sample to be receivedwhen the device is in a dim environment. Hence, as discussed above, theentire sample window is initialized to the greatest sample when thedevice 20 out of the holster.

If the screen 24 turns off due to a system timeout or the power buttonbeing pressed, but the device 20 has not been yet been turned off orreturned to its holster (step 110), then light sensor sampling revertsto sleep mode (step 100) provided the screen 24 does not turn back onwithin the time it takes to receive the next five samples. This fivesample delay is provided because the screen 24 may time out while theuser is reading the screen. It is common for a user to handle thissituation by hitting a key to immediately wake up the screen again(which turns on the backlight). In this case, the sample window is notreset to sleep mode. If the LCD screen 4 stays off for more than a fewseconds then the sample window is reset to sleep mode due to thelikelihood that the device environment has changed.

Based on the foregoing, LCD screen 24 brightness responds to a changefrom a dimmer to a brighter environment within 800 ms to 2 seconds. Thisis the amount of time that it takes to receive three brighter samples(which sets the median of the 5-sample window). The first sample in abrighter environment triggers the fast 400 ms sampling rate (step 104).However, it can take up to 1.2 seconds before the first sample isreceived. LCD screen 24 brightness responds to a change from a brighterenvironment to a dimmer mode in about 6 seconds. It takes 5 consecutivesamples in a dimmer mode to cause a transition to the new mode. When thescreen 24 backlight brightness is adjusted downwardly, the backlight isslowly faded to the new brightness level. This fading takes from about 1s to 1.5 s.

As discussed above in connection with FIG. 1, the light sensor andmessage indicating LED share a common light pipe. If the samplingalgorithm of FIG. 8 requires a light sensor sample to be taken while theLED is on, then the sample is delayed until immediately after the LEDturns off, unless the device 20 is in the process of being pulled out ofits holster. In this case, an initial low light sample is “faked” if theLED is on while removing the device 20 from its holster, etc. so as notto delay turning on the LCD screen 24 backlight (which cannot occuruntil a sample has been received). Each LED on/off transition iscontrolled so that the state information can be provided to theautomatic backlight software set forth herein of LED on/off transitions.

Preferably, coarse timers are used in the described method (e.g.+/−12.5% variance). The use of coarse timers minimizes the number oftimes the processor 36 must wake up due to timer events. Consequently,all times referred to in this specification are characterized by apossible error of +/−12.5%.

If the power button of device 20 is pressed, the screen 24 brightness isincreased significantly. This overrides the brightness adjustmentalgorithm temporarily until the screen is turned off, and normal screenbrightness adjustment resumes when the screen 24 turns back on again.

The light sensor functionality set forth herein may be altered ordisabled by the user via an “Automatic Backlight” option accessiblethrough a Screen/Keyboard options screen displayed by device 20. Thisenables backlight functionality which allows the user to press the powerbutton to cycle between 1) user-selected brightness; 2) super-bright;and 3) backlight/LCD off. When the LCD screen 24 is on, the keypad 34backlight is always on. When the LCD screen 24 is off, the keypad 34backlight is always off.

While the embodiments described herein are directed to particularimplementations of the method for automatically adjusting screen andkeypad brightness on a mobile handheld electronic device, it will beunderstood that modifications and variations to these embodiments arewithin the scope and sphere of the present application. For example, asindicated above the backlighting brightness adjustment methodology setforth herein is not limit in its application to handheld electronicdevices but may advantageously applied to other electronic devices suchas desktop computers, cellular telephones, GPS receivers, smarttelephones, and laptop computers. Also, it is contemplated that thekeypad backlighting, although independent of LCD screen backlightingadjustment, may advantageously transition between various lighting modes(such as DIM, OFFICE and BRIGHT) rather than simply switching between ONand OFF. Many other modifications and variations may occur to thoseskilled in the art. All such modifications and variations are believedto be within the sphere and scope of the present application.

1. A method for automatically adjusting screen and keypad brightness ona mobile electronic device having a light sensor, display screen andkeypad, comprising: obtaining light level samples from said lightsensor; and independently adjusting backlight intensity of said displayscreen and keypad responsive to said light level samples, whereinadjusting the backlight intensity of said display screen furtherincludes comparing a median value of said samples to respectivethreshold values corresponding to a DIM mode, wherein said backlightintensity is dimmed for low lighting environment, an OFFICE mode,wherein said backlight intensity is set to a brightness that is higherthan in said DIM mode and a BRIGHT mode of backlight intensity, whereinsaid backlight intensity is set at full brightness, and wherein saidbacklight intensity is adjusted from DIM mode to OFFICE mode in theevent said median value of said samples is greater than a firstthreshold, wherein said backlight intensity is adjusted from DIM mode toBRIGHT mode in the event said median value of said samples is greaterthan a second threshold, wherein said second threshold is greater thansaid first threshold, wherein said backlight intensity is adjusted fromOFFICE mode to DIM mode in the event said median value of said samplesis less than a third threshold, wherein said third threshold is lessthan said first threshold, wherein said backlight intensity is adjustedfrom OFFICE mode to BRIGHT mode in the event said median value of saidsamples is greater than said second threshold, wherein said backlightintensity is adjusted from BRIGHT mode to DIM mode in the event saidmedian value of said samples is less than said third threshold, andwherein said backlight intensity is adjusted from BRIGHT mode to OFFICEmode in the event said median value of said samples is less than afourth threshold, wherein said fourth threshold is intermediate saidfirst threshold and said second threshold, wherein the backlightintensity of said keypad is adjusted from an OFF mode to an ON mode inthe event a current light level sample is less than a fifth thresholdvalue, wherein said fifth threshold value is intermediate said firstthreshold and said third threshold and from an ON mode to an OFF mode inthe event said current light level sample is greater than a sixththreshold value for a predetermined time period, wherein said sixththreshold value is intermediate said first threshold value and saidfourth threshold value.
 2. The method of claim 1, wherein said fifththreshold value is approximately 60 Lux.
 3. The method of claim 2,wherein said sixth threshold value is approximately 250 Lux and saidpredetermined time period is approximately 30 seconds.
 4. The method ofclaim 1, wherein said light level samples are obtained at a firstsampling rate upon activation of said light sensor or in the event of atransition from said DIM mode to said OFFICE or BRIGHT modes or fromsaid OFFICE mode to said BRIGHT mode, and otherwise a second samplingrate.
 5. The method of claim 4, wherein said median value is calculatedfrom five consecutive ones of said light level samples.
 6. The method ofclaim 5 wherein said first sampling rate is maintained for five sampleswhereupon further light level samples are obtained at said secondsampling rate.
 7. The method of claim 6, wherein said first samplingrate is one sample per approximately 400 ms and said second samplingrate is one sample per approximately 1.2 ms.
 8. The method of claim 7,wherein said first and second sampling rates are each subject to avariance of approximately +/−12.5%.
 9. The method of claim 5, whereinsaid median value is calculated by sorting and selecting the third ofsaid five samples.
 10. The method of claim 1, wherein the backlightintensity of said keypad is adjusted from an ON mode to OFF mode inresponse to consecutive light level samples greater than said secondthreshold value for approximately 30 seconds.
 11. The method of claim 1wherein adjustment of the backlight intensity of said display screen andsaid keypad from brighter to dimmer is gradual whereas adjustment of thebacklight intensity of said display screen and said keypad from dimmerto brighter is quick.
 12. The method of claim 1, wherein said firstthreshold value is approximately 70 Lux, said second threshold value isapproximately 4400 Lux, said third threshold value is approximately 16Lux and said fourth threshold value is approximately 3000 Lux.